72 



ILLUSTRATIONS OF THE 



might be produced ; but in confequence of ^ 

 caufe which, like refrigeration, aded equally or^ 

 all the parts of the mafs, and preferved their 

 abfolute contad after their fluidity had ceafed. 

 66. A mark of fulion. or at 



mon 



r 



at leaft of the ope 

 f heat, which whinftone poflefles in com 



_ 1 



th many other minerals, is its being pe 



netrated by pyrites, a fubft 

 ready remtirked, that is of a 

 clufively the produdion of fi 



as has been al- 



thers moll ex- 



Another mark 



of fufion, more diftinaive of whin, is, that both 

 in veins and in malTes it fometimes includes pieces 

 of fandftone, or of the other contiguous ftrata, 

 completely infulated, and having the appearance 

 of fragments of rock, floating in a fluid fuffi- 

 ciently denfe and ponderous to fuflain their 



ght. Though thefe fragments h 



too refradlory to be reduced into 

 felves, they have not remained 



fufi 



been 



them- 



ely un- 



f 



changed, but are, in general, extremely indu 



d 



comparifon of the rock from 



hich 



they appear to have been detached 



Simila 



r 



infl;ances of extraordinary indu 



a 



oblerved in the 

 ith M 



of the ft 



hinftone, whether they form the 



fides of the veins, or the floors, and roofs of 



afles 



Th 



fl 



nto which the whinftone is diftributed, 

 :ata whether fandy or argillaceous, m 

 fuch fituations, are ufually extremely hard an4 



confolidated; 



y 



